Shielded cable, also known as armored cable and BX, consists of a spirally wound strip of metal that provides a relatively flexible duct in which conductor wires are protectively enclosed. For cutting such material to desired length, a saw cut must be made through the spirally wound strip, in a direction substantially lengthwise of the cable and having a length at least equal to the width of the spirally wound strip.
Although a hack saw is a commonly used tool for cutting shielded cable, it is not well suited for the purpose because the cable must be rather sharply flexed at the cutting zone and the hack saw blade must be applied to a surface on the cable that curves away from the blade edge in all directions and thus encourages the saw to slip off of the cable and possibly injure the person performing the operation. In addition, the depth of a cut through the shielding should be carefully controlled to avoid damage to insulation on the conductors inside it, but there is no reliable way to gage the depth to which a hack saw blade has penetrated the shielding.
With these considerations in mind, a number of devices for cutting shielded cable have heretofore been proposed, intended to afford safety both for the user and for the insulation on the conductors. Most such devices have comprised a circular saw blade that was rotated by means of a hand crank or the like, cooperating with a cable supporting means whereby the shielded cable was secured in such relation to the saw blade that the latter could penetrate the shielding to only a limited depth.
U.S. Pat. No. 2,654,941 discloses such a device wherein the cable supporting means comprises two elongated lengthwise spaced apart cradle sections, one to underlie the cable and support it, the other to overlie the cable and steady it. The cable is maneuvered between the two cradle sections and then swung into engagement with them. Under some conditions a shielded cable could probably be attached to this device, cut and removed from it with commendable speed and facility. However, the cable is not positively clamped to the device, and the flexing of a free length of shielded cable is difficult to control, so that there are situations in which the cable would control the position and orientation of the cutting device, rather than being controlled by it, and the cutting operation would therefore be awkward. A further and very important disadvantage of this device is that it can be used with shielded cable of only one diameter.
U.S. Pat. No. 2,674,027 discloses a device wherein the shielded cable to be cut must be slid lengthwise in an elongated substantially tubular holder to bring it to a position at which a cut is to be made in it, and the cable is clamped at that position by means of a thumb screw threaded into the holder transversely to its length. The device is obviously inconvenient to use when a cut must be made at a location some distance from each end of a long piece of cable.
U.S. Pat. No. 3,851,387 discloses a device having an elongated cable holder in the form of a trough that is open at one side, for lateral insertion of the cable to be cut, and the cable is again clamped in place by means of a thumb screw threaded into the holder. The disadvantage of this arrangement is that the thumb screw must be tightened into secure clamping relationship with the cable for a cutting operation and loosened after that operation is performed. Tightening and loosening of the thumb screw take time and require a certain amount of strength.
U.S. Pat. No. 3,633,275 discloses a device wherein the cable holder has hinged clamping jaws which require the operator to exert manual clamping force upon the cable with one hand while attending to actuation of the rotary cutting blade with the other hand. While securement and release of the cable can be effected rather quickly with this arrangement, the security with which the cable is locked to the device is dependent upon the strength of the operator's one hand. Use of this device can therefore be fatiguing, especially where several cuts must be made in rather rapid succession. Furthermore, the clamping holder is inherently suited only for larger diameter shielded cables; to adapt it for smaller diameter cables a small spacer must be fastened to one of the clamping jaws by means of a thumb screw. Installation of such a spacer is in itself time consuming and inconvenient, and because it is a relatively small part it can be easily lost or misplaced. Another important disadvantage of this device is that the saw blade is biased towards the cable by means of a spring that exerts a predetermined force which the user cannot vary during the course of a cut and which may be too great under some circumstances and too small at other times.
U.S. Pat. No. 3,453,917 discloses a device which is intended to be mounted on a workbench or the like and which therefore presents the inconvenience that, for every cut, the cable must be moved to the workbench or the workbench moved to the cable. The cable is clamped to the device by means of a thumb screw, so that securement and release of the cable are not convenient operations.
As correctly pointed out in some of the above-discussed patents, a cable cutter of the type here under consideration is essentially a safety device intended to protect the user against the hazards inherent in using a hack saw. Since a hack saw is almost invariably available to a person who has occasion to cut shielded cable, the cost of a cable cutter must be low enough not to discourage its purchase as a supplement to the hack saw. Furthermore, a hack saw can be brought into action on a piece of shielded cable practically instantaneously. Therefore, the problem is not just to provide a cable cutter that is low in cost, functionally satisfactory and reasonably convenient in use, but to provide a cable cutter which offers the user so much speed and convenience that he has no incentive to use the hack saw instead. Apparently this real problem has not heretofore been recognized, or else those skilled in the art have heretofore been unable to solve it; but in either case, as is apparent from the foregoing review of the prior art, it has not heretofore been obvious how to provide a shielded cable cutter that not only satisfies the obvious need for low cost, sturdiness and safety but also affords no less convenience and speed than a hack saw seems to offer.